This invention relates to an installation for charging a shaft furnace. More particularly, this invention relates to a shaft furnace charging apparatus of the type having a rotary or oscillating spout for distributing the charge material inside the furnace, comprising several containers for storing the charging material, a sluicing system for introducing the charge onto the distribution spout, and a valve cage which is mounted on the mouth of the furnace and has a flow duct controlled by a metering valve and a sealing valve.
Among the charging installations of this kind (usually referred to in the relevant art as "coneless throat" installations), there are generally two different types. The conventional type of installation is described in U.S. Pat. No. 3,693,812 ('812 patent) which is assigned to the assignee hereof. This apparatus has two storage containers above the furnace and arranged next to each other on either side of the vertical axis of the furnace. The two containers are connected by an inclined surface to a vertical flow duct above the distribution spout.
The second type of installation, which is more recent, is described in patent document EP-O-No. 062,770 corresponding to U.S. Pat. No. 4,514,129 ('129 Patent) assigned to the assignee hereof. This installation, which is more widely known in the art as a central feed installation, is characterized by two containers which are mounted one above the other symmetrically about the axis of the furnace. One of the containers acts as a sealing chamber.
Each of the two types of installations described above has its own advantages and drawbacks compared to the other type of installation. However, it will be understood the advantages of one are generally the drawbacks of the other and vice versa. Thus, one of the advantages of the conventional installation described in the '812 patent is that the two containers operate alternately, i.e., one is filled while the other one is emptied. This gives rise, aside from the relatively short time for operation of the valves as well as pressurization and depressurization, to an almost continuous charging operation. On the other hand, in the installation with two containers arranged one above the other described in the '129 patent, the charging operation must be interrupted during transfer of the charging material from the upper chamber to the lower chamber.
One of the drawbacks of the conventional installation ('812 patent) with two containers arranged next to each other is that the two containers must both be designed in the form of a lock chamber, thereby requiring, in addition to the two metering valves, two pairs of sealing valves. On the other hand, in the second type of installation ('129 patent), only one of the containers is in the form of a lock chamber, thereby reducing the number of sealing valves.
Another drawback of the installation with two chambers arranged next to each other ('812 patent) is that the flow of the charging material on the inclined surface provides the falling trajectory of the charging surface with a horizontal component, thereby altering the point of impact of the charging material on the distribution spout according to the position of the latter and depending on the chamber which is being emptied. Because of this phenomenon, irregular or asymmetrical distribution of the charging material inside the furnace results. On the other hand, in the type of installation with two containers arranged one above the other ('129 patent), the flow of charging material is vertical and symmetrical in relation to the central axis of the furnace, thereby permitting a more regular distribution inside the latter.
One of the drawbacks of the installation with two containers arranged one above the other ('129 patent), is its relatively significant height resulting from the arrangement of the containers one above the other. This is the reason why, in order to limit the overall height, there is a tendancy to provide containers which are wider and less high. However, the use of wider and shorter containers accentuates another known problem, i.e., that of separation of the particles inside the container according to their size. This phenomenon, which was considered in more detail in Luxembourg Patent Application No. 85/810 filed Mar. 15, 1986, becomes more marked as the diameter of the container increases and occurs more particularly in the second type of installation ('129 patent), since the separation effects inside each of the two containers are combined, thereby increasing the final separation effect. On the other hand, in the type of installation with two chambers arranged next to each other ('812 patent), the separation effect is less marked due to the fact that the chambers may be designed so as to be higher and less wide. Moreover, the separation effects inside the two chambers are not combined.